The solar cells with integrated bypass diodes are of particular interest in the manufacture of multilayer solar cell which are the subject of earlier commonly assigned Australian Patent Application No PM4834 entitled "Multiple Layer Thin Film Solar Cells" which is incorporated herein by reference.
In the prior art a bypass diode is a diode connected in reverse polarity to the diode which constitutes the solar cell. In normal practice, these bypass diodes are discrete diodes which are physically connected across individual cells or groups of cells by techniques such as soldering. In normal operation, these bypass diodes are reverse biased and do not interfere with cell operation. However, when cells have lower current output than others in the system, due to effects such as shadowing or cell damage, these diodes provide a low resistance path around the low output cells. This serves two functions. The first is to prevent excessive reverse voltage building across low output cells which can lead to cell destruction by overheating. The second role is to control the disproportionate loss of power output that such a shaded or damaged cell could introduce into the system of interconnected cells. The purpose and function of bypass diodes are well understood and widely discussed in standard texts such as Martin A. Green, "SOLAR CELLS: Operating Principles, Technology and System Applications", (Prentice-Hall, New Jersey, 1982) and S. R. Wenham, M. A. Green and M. Watt, "Applied Photovoltaics", (Bridge Printery, Sydney, 1994). Prior art integral bypass diodes serve a similar function although in general, due to their incorporation directly into the solar cell structure, lead to a reduction in the active volume of the cell with a corresponding reduction in performance even when the bypass diode is reverse biased.
Although bypass diodes are generally incorporated to provide protection and to decrease power losses during operation in the field, a new and advantageous application of the present invention is to use such diodes to maintain high production yields of modules of interconnected cells by providing automatic bypass of damaged or poorly performing cells within the module. One strategy, well suited to module fabrication where there is no prior testing of individual cells, is to include a small number of additional cells so that a guaranteed minimum output will be achieved even in the event of a small number of cell failures.